Optical scanners are well-known in the art and produce machine-readable data which is representative of the image of an object, e.g. a page of printed text. Optical scanners generally employ line-focus systems which image an object by sequentially focusing narrow "scan line" portions of the object onto a linear photosensor array by sweeping a scanning head over the object.
In a line-focus system, a light beam from an illuminated line object is imaged by a lens on a linear photosensor array which is positioned remotely from the line object. The linear photosensor array is a single dimension array of photoelements which correspond to small area locations on the line object. These small area locations on the line object are commonly referred to as "picture elements" or "pixels." In response to light from its corresponding pixel location on the line object, each photosensor pixel element in the linear photosensor array (sometimes referred to simply as "pixels") produces a data signal which is representative of the light intensity that it experiences during an immediately preceding interval of time known as a sampling interval. All of the photoelement data signals are received and processed by an appropriate data processing system.
A hand-held optical scanning device is an optical scanner which is moved across a scanned object, e.g. a page of text, by hand. Optical systems for hand-held scanning devices must generally be very compact due to the relatively small size of hand-held scanning devices.
Rollers may be provided on a hand-held scanning device to guide the device across the object to be scanned and also to provide data to the scanning device microprocessor regarding the speed at which the scanning device is being moved over the scanned object. These rollers may also serve to control the speed at which an operator moves the scanning device across the scanned object.
The construction and operation of hand-held optical scanning devices employing such rollers is disclosed in the following U.S. Pat. Nos.: 5,381,020 of Kochis et al. for HAND-HELD OPTICAL SCANNER WITH ONBOARD BATTERY RECHARGING ASSEMBLY and 5,306,908 of McConica et al. for MANUALLY OPERATED HAND-HELD OPTICAL SCANNER WITH TACTILE SPEED CONTROL ASSEMBLY (and corresponding EPO patent application no. 94301507.3 filed Mar. 2, 1994), which are all hereby specifically incorporated by reference for all that is disclosed therein.
In most hand-held optical scanning devices, the optical components and electronics of the scanning device are enclosed in a housing which is adapted to be grasped by the hand of a user while a scan is being performed. The housing generally also rotatably mounts the roller or rollers previously described.
In such scanning devices, it is generally desirable to completely seal the portion of the housing enclosing the optical components and electronics. The housing, sealed in this manner, prevents dust, moisture and other potential contaminants from entering the interior of the housing and contaminating the optical components and associated scanning device electronics.
Because the image beam from the object must pass through the housing to reach the optical components, a sealed housing, as described above, must be provided with a transparent window. This window is often constructed of glass and mounted in the bottom wall of the scanning device housing. In many cases, however, the window is formed of a transparent plastic material in order to reduce the overall weight of the scanning device.
In conventional hand-held scanning devices, the window is located such that it rests directly on the object being scanned and actually slides along the object when the scanning device is moved across the object to perform a scanning operation. The window sliding along the object is useful in that the window maintains the object, typically a document in a flat, stable position as the optics is directed toward the object. However, this presents a problem since such sliding contact between the window and the object often results in scratching of the window material. Although plastic windows are more prone to such scratching, glass windows may also be scratched. Such scratching may result, for example when the scanning device is moved across objects which are dirty or gritty or when a staple is encountered.
A scratched or otherwise damaged window will distort the image beam passing through the window and thus result in degradation of the quality of the image acquired by the hand-held scanning device.
Thus, it would be generally desirable to provide an apparatus which overcomes these problems associated with hand-held optical scanning devices.